The development of a simian model of fetal hematopoiesis permits a direct approach to measurement of fetal erythropoiesis and an assessment of the possible impact of erythropoietin in the selection of clones of erythroid precursors that are programmed to produce mainly hemoglobin F (BFU-Ef), hemoglobin F and A (BFU-Ef,a) and hemoglobin A (BFU-Ea). In addition, the model will permit investigation of improved systems for separation of fetal and adult cells for the purpose of enhancing prenatal diagnosis of hemoglobinopathies.